US Patent 7766480 Gonio lens with geometric reference

A gonio lens is provided including a contact lens element and a geometric reference member. The contact lens element has an optical axis, a concave posterior contact surface to be placed in optical contact with the cornea of a patient's eye, and an anterior surface. The geometric reference member, such as a scale, is provided near the concave posterior contact surface of the contact lens element. The configuration and location of the geometric reference member are chosen to provide an image of the geometric reference member adjacent to an image of the periphery of the anterior chamber of the eye of a patient within a field of view of the contact lens element when the contact lens element is placed on the eye of a patient. The two images are formed relative to each other such that they are simultaneously in focus to permit visual comparison between the two.